Electric signal amplifying apparatus

ABSTRACT

This invention is a signal amplifying apparatus which detects a magnetic flux generated in a magnetic core by an input signal and obtains such output as cancels it.

United States Patent [151 3,686,581 Takeda et al. [451 Aug. 22, 1972[541 ELECTRIC SIGNAL AMPLIFYING [58] Field of Search ..324/43 R; 330/63,8

APPARATUS [72] Inventors: lkuo Takeda, 2-24 Sekimachi; [56] Referencescued Takashi Suzuki, c/o Takeda Riken UNITED STATES PATENTS Industry Co.Ltd., l-chome, Asachicha; Hikam Fumkawa, 2296, 2,861,242 11/1958 Leavztt..324/43 ohoizumigakuemmachi, v n of 3,040,248 6/1962 Geyger.. ..324/43Nerimwku Tokyo, Japan 3,218,547 11/1965 Sung Chmg Lmg ..324/43 [22]Filed: March 31, 1970 Primary Examiner-Nathan Kaufman 2 L 24,210Attorney-William J. Daniel 3 57 ABSTRACT [30] Foreign ApplicationPriority Data i Y i ThlS invention 1s a signal ampllf ylng apparatusWhlCh Aprll 1, 1969 Japan ..44/24391 detectsa magnetic flux generated ina magnetic core t d b h t t l 52 us. Cl. ..330/63, 330/76, 330/188, ana1 0 mm Sue as 324/43 R [51] Int. Cl ..H03f 9/00 1 Claim, 1 DrawingFigure Patented Aug. 22, 1972 ELECTRIC SIGNAL AMPLIFYING APPARATUS Thisinvention relates to electric signal amplifying apparatus. In the caseof amplifying an electric signal,

generally vacuum tubes or transistors are used. However, as they arerestricted by shot noises and thermal noises of the circuit resistance,it is very difficult to amplify signals as minute as nanovolts withthem. A coupling is likely to be produced between the input and outputterminals through a feedback circuit, and it is difficult also tocompletely prevent mutual action with other signal systems.

An object of the present invention is to provide an amplifying apparatuswhich can easily amplify minute signals and at the same time,particularly, can completely isolate the input and output terminals fromeach other and from other signal systems.

The accompanying drawing is a circuit diagram of an embodiment of thepresent invention.

In the embodiment shown in the drawing, a magnetic core C is providedwith a signalwinding S, a feedback winding B and detecting windings Kand K having the same number of turns connected in series with reversepolarities so that oppositely directed magnetic fluxes may be generated.

The signal winding S is connected to a signal input terminal T Further,both ends of the detecting windings K and K which are oriented on thecore in the same direction are connected to opposite ends of thesecondary winding of a transformer M. The output of an oscillator O isapplied to the primary winding of this transformer M.

The oscillator sends out an output of a relatively high frequency, atleast more than twice as high as the signal frequency to be amplified.Further, the center tap of the secondary winding of the transformer Mand the common terminal of the detecting windings K and K arerespectively connected to the input terminals of a demodulator D so thatits input may be demodulated with the output of the oscillator O.

Its demodulated output is amplified with any amplifier A such as atransistor or vacuum tube, and this amplified output is applied to thefeedback winding B through a resistance. The output terminal of theabove mentioned amplifier A is also connected to an output terminal T2.

In the above described apparatus, if, for example, any direct currentsignal is applied to the terminal T an electric current flows in thesignal winding S and a magnetic flux in the direction corresponding tothe polarity of the current is generated in the magnetic core C.Therefore, when this magnetic flux is not generated, the impedances ofthe detecting windings K and K are symmetrical and therefore no input isdelivered to the demodulator. However, in the presence of the abovementioned direct current magnetic flux, an unbalance is caused in thesymmetry of the windings K, and K and a modulated input proportional tothe input signal is applied to the demodulator D. As this input isdemodulated with the output of the oscillator O, a direct currentvoltage having a polarity corresponding to the polarity of the inputsignal applied to the terminal T is delivered to the amplifier A. Asthis voltage is amplified and is applied the series circuit of thefeedback winding B and'resistance R, a direct current flows in saidwinding and magnetic flux is generated in the magnetic core C.

The winding B is connected to the output terminal of the amplifier A sothat its magnetic flux may be oppositely directed with to the magneticflux generated by the current in the signal winding S. Therefore, if theamplifier A has high enough gain, the magnetic fluxes generated by thewindings S and B will be stabilized and substantially canceled.

The output of the amplifier A in this state is delivered as the outputsignal from the terminals T That is to say, if the signal voltageapplied to the input terminal T, is e,, and the resistance of thewinding S is r,, a current i represented by 1 e 1/ r i l flows throughthe winding S. Further, if the output voltage of the amplifier A, thatis, the voltage appearing at the output terminals T is e the resistanceof the winding B is r and the value in the resistance R is r,,, the cur-.rent i of said winding B is represented by Therefore, if the numbers ofturns of the windings S and B are respectively n, and n the directcurrent magnetic field AH remaining in the magnetic core C isrepresented by As an input corresponding to this differential magneticfield AH is applied to the demodulator D, if the proper coefficient is Kand the gain of the amplifier A is a, the output voltage e of saidamplifier is represented y That is to say,

0/ 1 1/ 1- a o/( o+ 2) (s) is obtained from the above mentioned formulas(3) and (4). Therefore, if Ka is made large enough so that,

. o ("i/"2) o d fi'fi holds, then, by selecting the resistance r and theratio of the numbers of turns n to n to be large, the output voltage ewhich represents the input voltage e amplified by a fixed gain can beobtained.

As described above, the apparatus of the present invention serves todetect a magnetic flux generated in a magnetic core by an input signaland to obtain output at a level which will just cancel it.

Therefore, in this apparatus, there is no fear of deteriorating the SNratio by thermal noises or shot noises and, though there is a noisegenerated by the Barkhausen effect based on the non-continuous variationof the magnetization in the magnetic core, this noise is so small as tobe well below the thermal noise of a resistance smaller than severalohms.

Further, the input side and output side of the circuit are so perfectlyisolated from each other with respect of a direct current that there isno problem with common mode noise as in a conventional high sensitivityamplifier. Therefore, with the present apparatus, minute input voltageof the order of nanovolts can be amplified and, at the same time, thepotential relation level as between the input and output terminals canbe freely selected.

In the embodiment it was explained the manner in which a magnetic fluxdetecting winding could be used. However, the present invention can beaccomplished also by the use of other detecting means, for example aHall effect magnetic flux detecting element.

What is claimed is:

1. Amplifying apparatus for amplifying an electrical input signal :2comprising a non-saturating magnetic core, a signal winding having afirst number of turns n and a resistance r the winding being wound onthe core and connected to conduct current from said input signal andinduce an input flux in the core, a feedback winding having a secondnumber of turns n and a resistance r the winding being wound on the corein operative relationship with the first winding, amplifier meanscoupled through a resistance r to the feedback winding to pass currenttherethrough and induce a feedback flux in the core opposed to saidinput flux,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,686 v1 Dated August 22, 1972 Inventofls) Ikuo DA et a1 It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

In The Heading of the Patent, insert Assignee: Takeda Riken IndustryCompany Limited, Tokyo, Japan Signed and sealed this 13th day of March1973.

(SEAL) Attest:

EDWARD M.PLETCHER,JR. v ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents FORM PO-1050 (10-69) USCOMM-DC 60376-P69 n U.$. GOVERNMENTPRINTING OFFICE: I959 O366-3

1. Amplifying apparatus for amplifying an electrical input signal e1comprising a non-saturating magnetic core, a signal winding having afirst number of turns n1 and a resistance r1, the winding being wound onthe core and connected to conduct current from said input signal andinduce an input flux in the core, a feedback winding having a secondnumber of turns n2 and a resistance r2, the winding being wound on thecore in operative relationship with the first winding, amplifier meanscoupled through a resistance ro to the feedback winding to pass currenttherethrough and induce a feedback flux in the core opposed to saidinput flux, means including flux detecting winding means on the core fordetecting magnetic fluxes in said core induced by said signal andfeedback windings and operative to deliver a control signal to saidamplifier means to continuously maintain the resultant of said fluxes inthe core at zero, and apparatus output terminals connected to the outputof the amplifier means to deliver an output signal eo proportional tothe feedback current, the relative numbers of turns in the input andfeedback windings being different and the apparatus output signal beingrelated to its input signal such that eo (n1/n2) (ro + r2/r1) e1 .